1. Field of the Disclosure
The present disclosure relates to a method of controlling a single-phase voltage source AC/DC converting circuit capable of being applied to an interconnection device and an uninterruptible power source device being a power source of a power system.
2. Discussion of the Background Art
There has been known a single-phase voltage source AC/DC converter capable of supplying power as converting a direct current to an alternating current by automatically adjusting a voltage, a frequency and a phase to those of a power system which is to be connected with (for example, see Japanese Patent Application Laid-Open No. 2009-219263).
A single-phase voltage source AC/DC converter of Japanese Patent Application Laid-Open No. 2009-219263 operates such that power supplied from a DC side is converted to an alternating current and is output to a system as active power while power supplied from an AC side is converted to a direct current and is output to the DC side as active power.
Here, it is required that a constant DC voltage is input to the single-phase voltage source AC/DC converter of Japanese Patent Application Laid-Open No. 2009-219263.
Here, in a case that a DC device output DC voltage of which fluctuates like recently-popularized solar power generation is directly connected to the single-phase voltage source AC/DC converter of Japanese Patent Application Laid-Open No. 2009-219263, it becomes difficult to control AC output (i.e., a voltage, a frequency and a phase) when the DC voltage is decreased by a predetermined amount or more.
Meanwhile, there has been known an inverter capable of converting a direct current to an alternating current by controlling a fluctuating DC voltage (for example, see “A Novel Utility-Interactive Electrical Energy Storage System Making Use of Electrical Double-Layer Capacitors and an Error Tracking Mode PWM Converter”, (The Institute of Electrical Engineers of Japan, Industry Applications, Transactions, 118-12, December 1998)). FIG. 1 is a view illustrating an inverter described in “A Novel Utility-Interactive Electrical Energy Storage System Making Use of Electrical Double-Layer Capacitors and an Error Tracking Mode PWM Converter”, (The Institute of Electrical Engineers of Japan, Industry Applications, Transactions, 118-12, December 1998). FIG. 2 is a view illustrating details of an automatic voltage regulator (dc-AVR) in FIG. 1. A DC voltage command value VD* being a target value of a DC terminal voltage is set at the inverter in FIG. 1. The automatic voltage regulator inputs a signal of difference between the DC voltage command value VD* and a DC voltage detection value VD at the DC terminal to an amplifier having low pass characteristics. The automatic voltage regulator adds a DC current value at the DC terminal to the output of the amplifier (i.e., feedforward). Then, the automatic voltage regulator obtains a PWM command j(t) as multiplying a signal obtained in a feedforward manner by a reference sine wave signal (i.e., a PCC voltage) which is systematically synchronized. The automatic voltage regulator generates a gate signal based on the PWM signal j(t).
Here, since the difference between the detected DC voltage and the specified value is provided in a feedforward manner as the PWM command, the inverter of “A Novel Utility-Interactive Electrical Energy Storage System Making Use of Electrical Double-Layer Capacitors and an Error Tracking Mode PWM Converter” (The Institute of Electrical Engineers of Japan, Industry Applications, Transactions, 118-12, December 1998) cannot perform autonomous parallel operation.
As described above, the single-phase voltage source AC/DC converter of Japanese Patent Application Laid-Open No. 2009-219263 has a problem with inputting of a fluctuating DC voltage and the inverter of “A Novel Utility-Interactive Electrical Energy Storage System Making Use of Electrical Double-Layer Capacitors and an Error Tracking Mode PWM Converter” (The Institute of Electrical Engineers of Japan, Industry Applications, Transactions, 118-12, December 1998) has a problem of incapability of autonomous parallel operation.
In order to solve the above problems, an object of the present disclosure is to provide a method of controlling a single-phase voltage source AC/DC converting circuit included in a single-phase voltage source AC/DC converter capable of freely controlling reactive power and performing autonomous parallel operation while being capable of supporting DC voltage fluctuation.